Secondary recovery method

ABSTRACT

Significant improvement in the recovery of hydrocarbons from a subterranean hydrocarbon-bearing formation containing acidsoluble components is accomplished by injecting into the formation via an injection well drilled into a formation communicating with an adjacent producing well and containing acid-soluble components which may or may not have water-sensitive clays and shales included therein, an aqueous acidic solution of a compound hereinafter described whereupon the acid component reacts with the acid-soluble components of the formation creating passageways or enlarging existing passageways thus facilitating the flow of fluids therein and the compound prevents postprecipitation of dissolved salts and thereby increases the recovery of hydrocarbons from the formation through the adjacent producing well.

United States Patent [1 1 Shupe et a1.

[ Nov. 4, 1975 1 1 SECONDARY RECOVERY METHOD [75] Inventors: Russell D. Shupe; Jim Maddox, Jr.;

Jack F. Tate, all of Houston, Tex.

[52] US. Cl 166/271; 252/855 C; 252/855 D [51] Int. Cl. E21B 43/22; E21B 43/27 [58] Field of Search 166/271, 273-275, 166/307, 305 R; 252/855 D, 8.55 C

[56] References Cited UNITED STATES PATENTS 2,875,831 3/1959 Martin et al 166/275 X 3,240,271 3/1966 Ortloff 166/27'4 X 3,319,714 5/1967 Knox 166/307 3,434,545 3/1969 Bombardieri 166/307 3,572,440 3/1971 Hutchinson et a] 166/307 3,659,650 5/1972 Stratton 166/275 3,703,928 11/1972 Fulford... 166/274 3,791,446 2/1974 Tate 166/307 3,811,504 5/1974 Flournoy et a1. 166/274 X 3,831,679 8/1974 Presley et a1. 166/307 3,858,656 1/1975 Flournoy et a1. 166/274 Primary Examiner-Stephen J. Novosad Attorney, Agent, or FirmT. H. Whaley; C. G. Ries; James F. Young [57] ABSTRACT Significant improvement in the recovery of hydrocarbons from a subterranean hydrocarbon-bearing formation containing acid-soluble components is accomplished by injecting into the formation via an injection well drilled into a formation communicating with an adjacent producing well and containing acid-soluble components which may or may not have watersensitive clays and shales included therein, an aqueous acidic solution of a compound hereinafter described whereupon the acid component reacts with the acidsoluble components of the formation creating passageways or enlarging existing passageways thus facilitating the flow of fluids therein and the compound prevents post-precipitation of dissolved salts and thereby increases the recovery of hydrocarbons from the formation through the adjacent producing well.

9 Claims, No Drawings SECONDARY RECOVERY METHOD FIELD OF THE INVENTION This invention relates to a method for the recovery of hydrocarbons from subterranean hydrocarbon-bearing formations containing acid-soluble components in which the permeability'of the formation communicating between the producing well and adjacent injection well is increased by treating with an aqueous acidic solution of a compound as hereinafter described thereby facilitating the flow of fluids through the formation resulting in increased hydrocarbon recovery via the production well.

DESCRIPTION OF THE PRIOR ART In recovering oil from oil-bearing reservoirs it usually is possible to recover only a minor part of the original oil in place by the primary recovery methods which utilize the natural forces present in the reservoir. As a result, a variety of supplemental recovery techniques have been utilized to increase the recovery of oil from subterranean hydrocarbon-bearing reservoirs or formations. Although these supplemental techniques are commonly referred to as secondary recovery operations in fact they may be primary or tertiary in sequence of employment ln such techniques, a fluid is introduced into the formation in order to displace the oil therein to a suitable production system through which the oil may be withdrawn to the surface of the earth. Examples of displacing media include gas, aqueous liquids such as fresh water or brine, oil-miscible liquids such as butane, or a water and oil-miscible liquid such as an alcohol. Generally, the most promising of the secondary recovery techniques is concerned with the injection into the formation of an aqueous flooding medium either alone or in combination with other fluids.

In the application of these conventional procedures for the production of hydrocarbons from similar formations by the secondary recovery method of water-injection, one of the principal difficulties that has been encountered is the generally low production response realized because of the low permeabilities and the consequent low rate of water acceptance of the communicating formation. Thus, these unfavorably low responses both in injection rate and in overall production have led to the abandonment of hydrocarbon production by water-injection methods from many carbonate formations after only a minimal amount of the oil-in-place has been produced.

One of the remedial measures that has been used frequently to increase water-injectivity in formations containing acid-soluble components is acid-treating of injection wells to improve the permeability surrounding the injection well bore, and thereby increasing the flow capabilities of the formation in the vicinity of the injection well bore. These measures, however, may result in only a temporary response in production improvement.

In acidizing an injection well utilizing the commonly employed procedure a non-oxidizing mineral acid, such as hydrochloric acid, is introduced into the injection well, and through the application of sufficient pressure is forced into the adjacent formation, where it reacts with the acid-soluble components, particularly the carbonates to dissolve them to form the respective salt of the acid, carbon dioxide and water, thereby increasing the permeability of the formation adjacent the bore of 2 the injection well. The technique is not limited to application in formations of high acid solubility. Sandstone and gypsum-containing formations may require acidization if the injected water is unstable with respect to CaCO Fe(OI-I) or other salts.

If desired, the acidization may be carried out at an injection pressure sufficiently great to create fractures in the strata or formation which has the desired advantage of opening up passageways into the formation along which the acid can travel to more remote areas from the injection well bore. Conversely, fracturing a formation into which a displacing fluid is injected quite often is not desirable since sweep efficiency may be decreased. The salts formed upon neutralization of the acid are extensively wate soluble and may pass through the formation dissolved in the displacing fluid.

There are, however, troublesome complications attending the use of hydrochloric acid, or other similar non-oxidizing mineral acids. In the acidizing process, the following primary beneficial reaction occurs: CaCO: 2l-ICl CaCl H O CO l. Under the higher pressures required to conduct an acidization, the CO is dissolved in the reaction mixture consisting of spent acid and connate water: CO H O H CO H HCOJ 2H C0 The equilibria may be summarized and written: Ca( I-ICO CaCO H CO H O C0 1.

After acidization is complete, the well is often returned directly to injection, the reaction products of the dissolution being forced into the formation in a solution of the displacing fluid. As the fluid moves away from the well bore, pressure diminishes allowing dissolved gases such as CO to break out of solution, inducing insoluble carbonates, such as CaCO to postprecipitate.

Similarly, acid-dissolved iron salts may reprecipitate within the formation as hydrous iron oxides a distance from the well bore when pI-I rises due to exhaustion of the acid. In like manner, gypsum may precipitate if the injected fluid contains sulfate ion and if its temperature increases within the formation since the gypsum has an inverse solubility relationship. Precipitation of this type when it occurs within the capillaries of a tight formation can severely lessen the injection rate by plugging such capillaries. I

It is known that molecularly dehydrated polyphosphates, are effective in retarding CaCO precipitation. These polyphosphates are unsatisfactory in the method of the present invention because they undergo rapid hydrolysis in the presence of the mineral acid components. As a result, the scale inhibiting properties. of these polyphosphates are destroyed. In addition, one hydrolytic reaction product, the phosphate ion (P0 can precipitate with calcium +2 or barium ions present in the produced water, causing additional plugging or scale deposition and they further aggravate the problem. The so-called glassy phosphates are known scale inhibitors. However, these glassy phosphates are unsatisfactory because of their slight solubility in acidic media and the tendency to form objectionable hydrolytic reaction products.

It is also known to employ various organic polymers to prevent the precipitation of the mineral salts. Many of these polymeric materials are unstable in mineral acids. In such acidic media they undergo spontaneous depolymerization to an ineffective species. A representative polymeric material which undergoes such hydrolysis in the presence of acids is polyacrylamide. In addi- 3 tion, this polymer has a further disadvantage in that it is unstable in aqueous media at temperatures of about 250F. and upwards. Many wells that may be treated by the method of the present invention have bottom hole temperatures of 250-300F. or higher.

The chemically altered natural polymers and natural polymers themselves, are effective inhibitors to prevent the precipitation of mineral salts. However, some materials such as sodium carboxymethylcellulose precipitate or decompose in the presence of mineral acids. Other known sequestering agents such as citric or tartaric acids, and/or complexing agents such as ethylenediaminetetraacetic acid and its water-soluble salts are known inhibitors to prevent the deposition of boiler scale in aqueous media. However, such materials are not applicable in the method of the present invention because they are not appreciably surface active and do not adsorb on the formation face.

The primary object of the present invention is to provide a method for the improved recovery of hydrocarbon fluids from subterranean fluid-bearing formations wherein a composition comprising an aqueous acidic solution of a compound as hereinafter described is injected into a formation communicating between a producing well and an adjacent injection well, said formation containing acid-soluble components and in some instances also containing water-sensitive clays or shales, and whereafter the acid component of the said composition reacts with the acid-soluble components of the formation to increase permeability of the formation thereby facilitating the flow of fluids therethrough and the compound prevents the post-precipitation of compounds formed by the reaction of the acidic component with the formation.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a new and improved method for the recovery of hydrocarbons fromsubterranean hydrocarbon-bearing formations in which there is injected into the formation via an injection well drilled into a fonnation communicating with an adjacent producing well and containing acid-soluble components which may or may not have water-sensitive clays included therein, a composition comprising an aqueous acidic solution of a compound as hereinafter described which is capable of reacting with the acid-soluble components of the formation to increase the permeability and porosity thereof and the compound prevents precipitation of compounds formed by the said reaction of the acid component thereby permitting a substantial increase of production of hydrocarbons from the formation via the production well.

An advantage resulting in treating subterranean hydrocarbon-bearing formations having acid-soluble components therein with the aqueous acidic solution of the compound is that the post-precipitation of acid-dissolved salts is prevented or materially decreased. Such post-precipitation, whether it be of carbonates from evolution of CO from solution, hydrous iron oxides from a rise in pH, or of gypsum from an increase in formation temperature, can lead to plugging of formation capillaries and a consequent reduction of permeability. Such an event can reduce injectivity and accordingly the rate of production from adjacent wells.

DESCRIPTION OF THE INVENTION formation so as to increase substantially the flow capability of the formation and to thereafter produce hydrocarbons from the said subterranean formation at an increased rate through the production well.

The compound useful in preparing the aqueous acidic solution of the present invention is a water-soluble sulfonated, ethoxylated, alkylphenol, having the following general formula:

wherein R is alkaryl, containing from about 6 to l8 carbon atoms in the alkyl portion thereof, n is a number from one to 10 including fractions, and A is a monovalent cation such as sodium, potassium or ammonium, including mixtures.

Representative examples useful in the practice of the invention include the straight and branched chain alkylphenols such as the hexyl-, isohexyl-, heptyl-, octyl-, isooctyl-, nonyl-, decyl-, dodecyl-, tridecyl-, tetradecyland hexadecyl-, species, containing one or more ethoxy groups attached to the alkylphenols; for example,

the di-, tri-, tetra-, penta-, hexa-, octa-, nona-, and decaethoxy compounds which have been sulfonated. A preferred group of compounds include the sodium and ammonium salts of sulfonated C -C, alkylphenols containing from about 3 to about 10 ethoxy groups therein.

Preferably, the acidic aqueous treating composition of this invention injected into the hydrocarbon-bearing formation comprises an aqueous solution of from about 0.01 percent to about 5 percent, preferably 1 percent to 3 percent by weight of carbon dioxide and which contains therein between from about 0.005 percent to about 2 percent by weight, preferably from about 0.05 percent to 1 percent of the aforesaid compound.

In the first step of preparing the aqueous acidic composition of this invention, a solution containing from about 0.01 percent to about 5 percent by weight of carbon dioxide in water is prepared. The required amount of the compound is then admixed with the aqueous acid solution.

The method of this invention can be carried out with a wide variety of injection and production systems which will comprise one or more wells penetrating the producing strata or formation. Such wells may be located and spaced in a variety of patterns which are well-known to those skilled in the art. For example, the

so-called line flood pattern may be used, in which case the injection and producing systems are composed of rows of wells spaced from one another. The recovery zone, i.e., that portion of the producing formation from which hydrocarbons are displaced by the drive fluid to the production system, in this instance will be that part of the formation underlying the area between the spaced rows. Another pattern which is frequently used is the so-called circular flood in which the injection system comprises a central injection well while the production system comprises a plurality of production wells spaced about the injection well. Likewise, the injection and production systems each may consist of only a single well and here the recovery zone will be that part of the producing strata underlying an elliptical-like area between the two wells which is subject to the displacing action of the aqueous drive fluid. For a more elaborate description of such recovery patterns reference is made to Uren, L.C., Petroleum Production Engineering-Oil Field Exploitation, Second Edition, McGraw Hill Book Company, Inc., New York, 1939, and to US. Pat. Nos. 3,472,318 and 3,476,182.

In carrying out the method of this invention, the aqueous acidic solution of the compound is forced, usually via a suitable pumping system, down the well bore of an injection well and into the producing formation through which it is then displaced together with hydrocarbons of the formation' in the direction of a production well. As those skilled in the art will readily understand, the pressure employed is determined by the nature of the formation, viscosity of the fluid, and other operating variables. The method of this invention may be carried out at a pressure sufficient merely to penetrate the formation or it may be'of sufiicient magnitude to overcome the weight of the overburden and create fractures in the formation. Propping agents, to prop open the fractures as created, for example to 60 mesh sand, in accordance with known fracturing procedures, may be also employed with the aqueous acidic solution containing the admixture.

The formation may be treated continuously with the resulting solution or such treatment may be temporary.

If desired, however, after a time, conventional flooding may be resumed. The aqueous acidic solution of the compound also may be applied in a modified water flood operation in which there is first injected into the well bore a slug of the aqueous acidic solution of the compound which is forced under'pressure into the subterranean formation. This first stepis then followed by a similar injection step wherein a slug of an aqueous drive fluid, such as water, is injected, which is thereafter followed by a repetition of the two steps. This sequence may be repeated to give a continuous cyclic process. The size of the slugs may be varied within rather wide limits and will depend'on a number of conditions, including the thickness or the formation, its characteristics and the conditions for the subsequent injection of the aqueous drive medium.

In the method of this invention, the compound of the composition provides means whereby ions produced by the reaction of the acid component with the formation having tendencies to precipitate as salts such as CaCO hydrous iron oxide and CaSO 2H2O combine with the compound moiety to form a highly stable complex therewith so that solid calcium carbonate does not precipitate from the spent treating solution. This binding up of the aforementioned calcium ions from weakly ionizable compounds permits the formed complex to remain dissolved in the treating soltuion and pass through the formation pores. Further, the compound of the composition provides means whereby the nucleation and growth of the solid itself is thwarted, so that solid salts do not precipitate from the spent treating solution. Finally, the compound of the composition provides means whereby continuous protection against post-precipitation of slats is obtained for a considerable period of time subsequent to treatment due to continuous slow desorption of the compound from the formation faces. In contrast, use of surfactants having merely dispersant and suspending properties and not possessing the capability of molecularly binding up these pro- 6 duced ions or thwarting the nucleation and growth of solid salts thereof will permit post-precipitation of said salts from such treating solution with the likelihood of plugging up the formation passageways during subsequent recovery of desirable formation hydrocarbons therethrough.

It should be understood that the concentrations of the compound and the acid component of the composition are chosen to provide a displacing fluid of the desired rheological properties. Similarly, the appropriate compound is selected on the basis of the formation being treated as well as other operating conditions employed.

The method of the present invention also finds applicability in combination with subsequent treatment of the formation using a polymeric mobility control agent in aqueous solution introduced therein through an injection well to minimize viscous fingering and to enhance volumetric sweep efficiency. Suitable mobility control agents are well known in the art such as the hydrophilic polymers of the polyacrylamides or the polysaccharides which can be used in amounts of from about 0.01 percent to about 0.1 percent by weight.

The method can be varied to employ injection of a large slug of the aqueous acidic solution of the compound followed by the aqueous solution of the polymeric mobility control agent, then followed by water injection. Repetitive treatments of one or all of these steps are within the purview of the invention. Additionally and/or optionally one may inject gaseous carbon dioxide after any or all of these slug treatments, to impart enhanced mobility to the oil by decreasing its viscosity, through the injection w'ell.

Following is a description by way of example of a method for carrying out the method of the present invention.

EXAMPLE I Through a water injection well drilled into a limestone formation there is displaced under pressure down the tubing and into the formation an aqueous acidic solution containing 1 percent by weight of carbon dioxide and 1 percent by weight of the compound, sulfonated pentaethoxy nonylphenol, sodium salt. The pressure required to inject the required volume of water declines considerably and no increase in said pressure is noted subsequent to treatment, indicating that post precipitation of CaCO within the formation leading to permeability reduction is prevented or materially lessened. The well is then returned to conventional water injection. After about 8 months the production of hydrocarbons from an adjacent producing well is substantially increased.

EXAMPLE II A flooding operation is carried out in a oil-containing reservoir in accordance with the process of this invention. Four injection wells are arranged in a rectangular pattern around a single centrally located production well in this system. A slug consisting of barrels of an aqueous acidic solution containing 2 percent by weight of carbon dioxide and 0.5 percent by weight of the same compound as Example I is displaced via each of the four injection wells into the formation at a rate of about 50 bbl/day. In the next step, barrels of water are injected under pressure into the producing formation through each injection well at a rate of about 55 bbl/day. This sequence of operations is repeated nu- 7 merous times and the result is an increased injection rate of the drive streams into the injection wells and a subsequent increase in the rate of production of hydrocarbons via the production well.

EXAMPLE III An injection well in a formation containing about 30 percent l-lCl-soluble material is treated with 1,500 gallons of 1.5 percent aqueous carbon dioxide containing 0.4 percent by weight of the compound of Example I. The aqueous acidic solution is displaced from the tubing into the formation with lease water and the well shut in for 24 hours. Thereafter the well is returned to water injection. The injectivity of the well is materially increased for a sustained period of time resulting in enhanced hydrocarbon recovery.

EXAMPLES IV-XII The procedure of Examples l-Ill is repeated using: Examples lV-VI Sulfonated pentaethoxy dodecylphenol, sodium salt.

Examples VII-IX Sulfonated pentaethoxy pentadecylphenol, sodium salt.

Examples X-Xll Sulfonated heptaethoxy pentadecylphenol, sodium salt.

It is significant that the compounds are effective in the presence of high calcium ion concentrations to 1 percent by weight or more, and particularly and somewhat uniquely in applications where high aqueous solution temperatures are encountered such as above 100C. Laboratory thermal stability tests reveal that the compound of Examples lV-VI remains 97.5 percent active after exposure of its aqueous solution to a temperature of 177C. for 5 days.

The disclosed compositions may be prepared in the following manner:

The polyethoxy alkylphenol is treated with thionyl chloride for about 18 hours at about 100C., to form the monochloro derivative, followed by reaction of said monochloro derivative with sodium sulfite for about 18 hours at about 155C, in a l/ 1 by volume admixture of water and ethanol in a Paar Bomb. The resulting recovered sulfonated product, on analysis, showed about 75 percent sulfonation of the terminal ethoxy group. This method of preparation is exemplary only, but was the method employed to prepare the tested compositions. Those skilled in the art may perceive other synthetic schemes. For example, a sulfated ethoxylated alkylphenol may be treated with sodium sulfite at 200C. for about -12 hours, resulting in relatively high yields (75-80 percent) of the desired sulfonated ethoxylated alkylphenol. Direct reaction of the ethoxylated alkylphenol and mixtures thereof with such reagents as sulfuric acid or chlorosulfonic acid results in sulfation.

Obviously, other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A method for the recovery of hydrocarbons from a hydrocarbon-bearing formation containing acid-soluble components having at least one injection well and at least one production well penetrating the said formation and in fluid communication, which comprises displacing through the formation a composition comprising an aqueous acidic solution containing from about 0.01 percent to about 5 percent by weight of carbon dioxide and from about 0.005 percent to about 2 percent by weight of a compound therein, said compound being a water-soluble sulfonated, ethoxylated compound having the general formula:

wherein R is alkaryl containing from about 6 to 18 carbon atoms in the alkyl portion thereof, 11 is a number from one to about 10 including fractions, and A* is a monovalent cation selected from the group sodium, potassium, and ammonium, including mixtures.

2. Method as claimed in claim 1, wherein said compound is present in said aqueous acidic solution in an amount of from about 0.05 percent to about 1 percent by weight.

3. Method as claimed in claim 1, wherein said compound is the sodium salt of sulfonated pentaethoxy mpentadecylphenol.

4. Method as claimed in claim 1, wherein said compound is the sodium salt of sulfonated pentaethoxy dodecylphenol.

5. Method as claimed in claim 1, wherein said compound is the sodium salt of sulfonated heptaethoxy mpentadecylphenol.

6. Method as claimed in claim 1, wherein said carbon dioxide is present in an amount of from about 1 percent to about 3 percent by weight.

7. Method as claimed in claim 1, wherein said solution is injected down the injection well bore penetrating said formation under a pressure greater than the formation pressure and sufficient to create fractures in the formation.

8. Method as claimed in claim 1, wherein said solution is injected down the well bore penetrating said formation under a pressure greater than formation pressure but less than the pressure required to create fractures in the formation.

9. Method for the recovery of hydrocarbons from a hydrocarbon-bearing formation containing acid-soluble components and having at least one injection well and at least one production well penetrating the said formation in fluid communication, which comprises displacing through the formation a slug of an aqueous acidic solution of from about 0.01 percent to about 5 percent by weight of carbon dioxide containing therein from about 0.005 percent to about 2 percent by weight of a compound, said compound being the sodium salt of sulfonated pentaethoxy dodecylphenol, thereafter injecting a slug of an aqueous drive fluid into the formation to drive the said composition through said formation toward said production well and recovering hydrocarbons through the production well. 

1. A METHOD FOR THE RECOVERY OF HYDROCARBONS FROM A HYDROCARBON-BEARING FORMATION CONTAINING ACID-SOLUBLE COMPONENTS HAVING AT LEAST ONE INJECTION WELL AND AT LEAST ONE PRODUCTION WELL PENETRATING THE SAID FORMATION AND IN FLUID COMMUNICATION, WHICH COMPRISES DISPLACING THROUGH THE FORMATION A COMPOSITION COMPRISING AN AQUEOUS ACIDIC SOLUTION CONTAINING FROM ABOUT 0.01 PERCENT TO ABOUT 5 PERCENT BY WEIGHT OF CARBON DIOXIDE AND FROM ABOUT 0.005 PERCENT TO ABOUT 2 PERCENT BY WEIGHT OF A COMPOUND THEREIN, SAID COMPOUND BEING A WATER-SOLUBLE SULFONATED, ETHOXYLATED COMPOUND HAVING THE GENERAL FORMULA:
 2. Method as claimed in claim 1, wherein said compound is present in said aqueous acidic solution in an amount of from about 0.05 percent to about 1 percent by weight.
 3. Method as claimed in claim 1, wherein said compound is the sodium salt of sulfonated pentaethoxy m-pentadecylphenol.
 4. Method as claimed in claim 1, wherein said compound is the sodium salt of sulfonated pentaethoxy dodecylphenol.
 5. Method as claimed in claim 1, wherein said compound is the sodium salt of sulfonated heptaethoxy m-pentadecylphenol.
 6. Method as claimed in claim 1, wherein said carbon dioxide is present in an amount of from about 1 percent to about 3 percent by weight.
 7. Method as claimed in claim 1, wherein said solution is injected down the injection well bore penetrating said formation under a pressure greater than the formation pressure and sufficient to create fractures in the formation.
 8. Method as claimed in claim 1, wherein said solution is injected down the well bore penetrating said formation under a pressure greater than formation pressure but less than the pressure required to create fractures in the formation.
 9. Method for the recovery of hydrocarbons from a hydrocarbon-bearing formation containing aCid-soluble components and having at least one injection well and at least one production well penetrating the said formation in fluid communication, which comprises displacing through the formation a slug of an aqueous acidic solution of from about 0.01 percent to about 5 percent by weight of carbon dioxide containing therein from about 0.005 percent to about 2 percent by weight of a compound, said compound being the sodium salt of sulfonated pentaethoxy dodecylphenol, thereafter injecting a slug of an aqueous drive fluid into the formation to drive the said composition through said formation toward said production well and recovering hydrocarbons through the production well. 